1. Field of the Invention
This invention involves a system and a method for presenting ultrasonic scan data acoustically to a user.
2. Description of the Related Art
Various imaging systems such as magnetic resonance imaging (MRI), CT scans, and medical ultrasound have greatly improved the ability to sense the internal structures of human bodies. These imaging systems have provided valuable diagnostic information for various diseases and pathologies and to date the preferred way of presenting information derived from imaging has been visual. In medical ultrasound, however, the Doppler wave form has been presented as a stream of stereo sound through a pair of left-right speakers; such an acoustic display has played an important part in the diagnostic process.
With the rapid progress in computational circuitry, modem ultrasound scanners have become ever more complex and powerful and have been able to acquire and process much more data from each scan. As computational power increases, so too does the need for more effective ways of presenting the ever-richer information available to the sonographer. The most effective way to present complex information to a human is to engage more than one sense: for example, hearing and touch as well as sight. Next to sight, sound information is the easiest to control and present and is best for effectively conveying information.
Psychoacoustic and psychological studies have indicated that audio information is particularly well suited for monitoring state changes over time and that hearing is a primarily time-dependent sense--one can easily hear a gradual change of tone in music but cannot as easily discern a gradual change in brightness of light. Audio signals are, moreover, detected more quickly than visual signals and they tend to cause more alerting and orienting responses. This feature of human physiology quickly brings a new sound event to our attention and also allows us to "filter out" sustained or uninteresting sounds and relegate them to the background. This is known as the "cocktail party effect": one can normally concentrate on and hear a juicy conversation even over the drone of a fan and the voice of a chatty, boring fellow guest.
One's keen sense of hearing and ability to discriminate sounds is especially useful in improving the intelligibility of noise sources and in segregating multiple sound sources. Various acoustic features such as temporal onsets and stops, timbre, pitch, intensity and rhythm can specify the identity of sound objects and convey meaning about discrete events or ongoing actions. Even the simple left-right stereo presentation of ultrasonic scan data has proven to be very helpful in indicating changes in, for example, cardiac blood flow, to the sonographer.
One other advantage of presenting information in the form of sound is that one does not need to be looking at a display screen in order to receive useful information. This is especially helpful during an ultrasonic scan of a patient, since the operator must otherwise look away frequently from the area where she is holding the transducer to see what is being presented visually on the screen.
One drawback of existing acoustic displays of ultrasound scan data is that they are purely "linear," with the apparent source always lying on a line between the user's ears. This is a gross simplification, since the flow velocity vectors one is attempting to "hear" usually have components in at least two dimensions, not just one. Like listening over stereo headphones to the recorded music of a large orchestra, one gets no feeling of depth, only of left and right.
What is needed is therefore a system for displaying ultrasonic scan data acoustically in such a way that a sonographer's ability to localize sound sources in more than one dimension is put to use, so that more of the information obtained from the ultrasound scan is discernible. The system should also allow the user to use both sight and hearing to receive and interpret the scan data.